In the field of mobile communication, a variety of information such as image and data in addition to voice becomes transmission targets in recent years. Accompanying this, the demand for higher reliability and high-speed transmission has increased. However, when high-speed transmission is carried out in mobile communications, influence of delayed waves due to multipath cannot be ignored, and so transmission performances deteriorate due to frequency selective fading.
As one of countermeasure techniques for frequency selective fading, multicarrier communication represented by the OFDM (Orthogonal Frequency Division Multiplexing) scheme becomes a focus of attention. A multicarrier communication is a technique of carrying out high-speed transmission by transmitting data using a plurality of subcarriers of which transmission speed are suppressed to an extent that frequency selective fading is not generated. Particularly, in the OFDM scheme, frequencies of a plurality of subcarriers where data is allocated are orthogonal to each other, so that it is possible to achieve optimal frequency efficiency in multicarrier communication schemes and realize the OFDM scheme in a relatively simple hardware configuration. Consequently, the OFDM scheme is focused upon as a communication method for use for a cellular-based mobile communication system, and is studied in various ways.
Studies are conducted for performing frequency scheduling transmission using the OFDM scheme on the downlink (see Non-Patent Document 1). In this frequency scheduling, a radio communication base station apparatus (hereinafter simply “base station”) adaptively allocates subcarriers to a radio communication mobile station apparatus (hereinafter simply “mobile station”), based on received quality of each frequency band in each mobile station, so that it is possible to obtain maximal multi-user diversity gain, thereby enabling extremely efficient communication. Such a frequency scheduling transmission scheme is primarily suitable for data transmissions when a mobile station moves at low speed.
Consequently, to perform frequency scheduling, each mobile station needs to report received quality to a base station for every subcarrier or every resource block which bundles a plurality of subcarriers. Normally received quality is reported by CQI (Channel Quality Indicator).
Here, if a mobile station reports CQI's for all subcarriers, uplink resources used for transmitting CQI become enormous, and, consequently, uplink data transmission capacity decreases. Now, a technique is proposed whereby a plurality of subcarriers are divided into a plurality of groups (i.e., a subcarrier group) and each mobile station reports the CQI for only one of subcarrier groups allocated to the mobile station, so that the amount of CQI transmission can be reduced (see Non-Patent Document 2). In addition, a subcarrier group will be abbreviated as a “SC group” in the explanation below.
Non-Patent Document 1: R1-050604 “Downlink Channelization and Multiplexing for EUTRA” 3GPP TSG RAN WG1 Ad Hoc on LTE, Sophia Antipolis, France, 20-21 Jun. 2005.
Non-Patent Document 2: R1-050590 “Physical Channels and Multiplexing in Evolved UTRA Downlink” 3GPP TSG RAN WG1 Ad Hoc on LTE, Sophia Antipolis, France, 20-21 Jun. 2005.